The martensitic transition temperature (MTT) of a shape-memory alloy (SMA) is one of its most important characteristics, determining its operating temperature, while the energy difference ($\mathrm{\Delta }E$) between the austenite and martensite phases is among the most crucial factors dictating MTT. Using density-functional theory, $\mathrm{\Delta }E$ of NiTi, the most studied and commonly used SMA, varies from 23 to 116 meV/atom, depending on the density functional [Wu and Lawson, J. Chem. Phys. 161, 134104 (2024)]. Consequently, free-energy calculations using different density functionals yield MTTs that differ by several hundred K. Here, we benchmark $\mathrm{\Delta }E$ of NiTi using diffusion quantum Monte Carlo. With this method, the energy difference is estimated to be $70.9\pm 2.5$ meV/atom.

Detailing emergent quantum phenomena predicted for hydrogen at high densities remains a key challenge in condensed matter physics. A first-order issue is stabilization of the quantum fluid relative to solid phases at multimegabar $(>100\mathrm{GPa})$ pressures, a problem for which accurate large-scale simulations can play a critical role in predicting behavior beyond the range of current pressure-temperature $\left(P\text{−}T\right)$ experiments. Here, we developed a machine-learned interatomic potential for hydrogen trained on accurate diffusion quantum Monte Carlo data, including total energies and atomic forces, which allows us to investigate the melting curve of hydrogen over a broad range of pressures. Our simulations predict a broad melting maximum near 1000 K at $100–150\mathrm{GPa}$, followed by a leveling off in the melting temperature at higher pressure, in good agreement with experiment. Beyond the range of current experiments, the simulations predict that hydrogen melts near room temperature and is remarkably independent of pressure from 500 to 900 GPa. Our results suggest that hydrogen does not have a fluid ground state up to terapascal pressure and provide a baseline for understanding this exotic quantum material at ultrahigh pressures.

The nonintegrable transverse-field Ising model is a common platform for studying ergodic quantum dynamics. In this work, we introduce a simple variant of the model in which this ergodic behavior is suppressed in the finite-size regime by introducing a spatial inhomogeneity in the interaction strengths. For this we partition the chain into two equal segments within which the spins interact with different coupling strengths. The ratio of these couplings defines an inhomogeneity parameter, whose variation away from unity leads to the mentioned constrained dynamics. We characterize this crossover using multiple diagnostics, such as the long-time saturation of out-of-time-ordered correlators, level-spacing statistics, and the spectral form factor. Making use of this tunable ergodic behavior, we can examine the impact of dynamical features towards operator spreading in the Krylov space and also for entanglement generation in the system's eigenstates. Unlike the monotonic behavior of the aforementioned diagnostics, the saturation of Krylov complexity shows a nontrivial suppression near the onset of constrained dynamics, which can be explained by quantifying the spread of the initial operator in the Krylov space. Together, these results demonstrate that introducing a macroscopic inhomogeneity in coupling strengths provides a minimal, disorder-free route to constraining the ergodic nature in this specific model of interacting spins, particularly in the finite-size regime. These effects are prominently reflected in a Krylov space analysis.

Disordered nonlinear systems have long been central to studies of complex dynamical behavior, yet most studies focus on spatial randomness. In contrast, when disorder fluctuates temporally, it drives the system far from equilibrium, giving rise to fundamentally different dynamical behaviors. Here, we investigate a nonlinear dispersive system subject to correlated temporal disorder, revealing how the interplay between dispersion and temporal disorder reshapes its dynamical phases. By analyzing correlation dynamics and replica-overlap statistics, we identify a transition from ergodic to nonergodic clustering, marked by distinct correlation patterns and symmetry breaking in replica statistics. These results clarify the statistical mechanics underlying temporally disordered nonlinear waves and provide insight into nonequilibrium phase organization in time-varying photonic systems.

We investigate dynamical quantum phase transitions (DQPTs) in generic Dirac Hamiltonians following a sudden quench. By deriving an exact analytical expression for the Loschmidt amplitude (LA), we establish a universal criterion for DQPTs in this broad class of systems. We introduce first- and second-order dynamical topological order parameters (DTOPs) to characterize DQPTs. Geometrically, the second-order DTOPs track the evolution of (d-2)-dimensional topological defects on a special (d-1)-dimensional surface dictated by the universal criterion. In the short-time regime, we uncover a direct link between three distinct phenomena: the reconfiguration of topological defects, the emergence of van Hove singularities in the density of LA zeros, and non-analyticities in the rate function. In the long-time limit, the defects coalesce into a dense domain-wall structure on the (d-1)-dimensional surface. We show that this critical surface is inherent to both the time-averaged pseudospin polarization and the Hamiltonian. Our general framework is validated through its application to a three-dimensional four-band Dirac model. These results provide a theoretical foundation for studying DQPTs in topological systems, particularly in higher dimensions. The developed methodology is directly extendable to other quench protocols and to non-Hermitian generalizations of Dirac Hamiltonians.

The interpretation of high harmonic generation (HHG) in solids typically relies on phenomenological dephasing times far shorter than what is expected from microscopic scattering processes. Here we show that zero-point fluctuations associated with optical phonons naturally suppress long-range electronic coherences and generate clean harmonic spectra without introducing ad hoc decoherence parameters. Using a one-dimensional semiconductor composed of two distinct sites per unit cell and realistic phonon amplitudes, we demonstrate that random per-site optical-phonon jitter reproduces the spectral sharpening typically attributed to ultrafast $T_2$ dephasing. In contrast, acoustic phonons and local strain, whose distortions are correlated over nanometer scales, produce negligible spectral cleaning. We further show that such long-range site coherence leads to carrier-envelope-phase (CEP)-dependent effects in the HHG spectrum driven by long pulses, but these effects are lost once optical-phonon-induced decoherence is included. Our results (i) identify optical zero-point motion as a key mechanism governing coherence in solid-state HHG, (ii) demonstrate that it can be qualitatively modeled in periodic solids through site-distance-dependent dephasing, and (iii) suggest that CEP-resolved measurements can probe electronic coherence lengths and atomic fluctuations in crystalline materials.

Host-guest crystalline materials with strong anharmonicity exhibiting long-range order and local disorder offer a paradigm for ideal thermoelectric model known as the “phonon-glass electron-crystal” (PGEC), which ensures efficient electrical conduction characteristic of crystals while suppressing thermal transport in a glasslike manner. It is widely accepted that guest atoms introduce low-frequency low-lying optical phonons (referred to as rattling modes), which intensely scatter the acoustic phonons, thereby drastically reducing lattice thermal conductivity (${\kappa }_L$). In quasi-one-dimensional (Q-1D) thermoelectrics, this mechanism is conceptualized as covalent 1D chains forming the host framework, with isolated interchain ions acting as charge-balancing rattlers to further dampen ${\kappa }_L$. However, our first-principles studies of the Q-1D perovskite $\delta \text{−}\mathrm{CsSn}{\mathrm{I}}_3$ reveal that the covalent 1D chains serving as host frames also produce low-lying optical phonons, which introduce additional three-phonon scattering channels. Utilizing self-consistent phonon theory and Wigner transport formalism, we capture phonon frequency renormalization and wavelike coherent scattering. This approach uncovers an ultralow ${\kappa }_L$ with weak temperature dependence, consistent with the results from homogeneous nonequilibrium molecular dynamics. Furthermore, based on a low-order expansion of electron-phonon coupling, we estimate a thermoelectric figure of merit $\mathit{ZT}$ up to 0.53 (0.92) at 300 (425) K for $\delta \text{−}\mathrm{CsSn}{\mathrm{I}}_3$. Notably, we identify the low-lying optical branches originating from the antiparallel sliding of the host 1D chains, offering additional phonon scattering channels for damping phonon transport. These findings offer new microscopic insights into Q-1D thermoelectric transport and provide a viable material platform and a design scheme to explore PGEC behavior in anisotropic systems.

We investigate a quasiperiodically driven four-level system that serves as a temporal analog of topological phenomena found in four-band models with intertwined spin and orbital degrees of freedom. Under a two-tone drive in the strong-driving regime, the system realizes a two-dimensional synthetic Floquet lattice, thus facilitating the realization of topological energy pumping. For a temporal quantum spin Hall insulator, we find that the rates of emission and absorption of energy between the two drives are not exactly opposite for a given band. However, when contributions from two chiral symmetric partner bands are added, they become exactly opposite. This quantized rate of energy exchange is a direct consequence of propagating edge modes in the real-space model, which we further characterize by computing the spin-Chern number. Interestingly, our analysis yields a zero rate of exchange of energy between the drives for a temporally higher-order topological insulator, suggesting the presence of localized corner modes that we characterize by the mid-gap Wannier spectra. Our findings uncover the role of chiral, particle-hole, and time reversal symmetries on the energy dynamics in temporal quantum spin Hall and higher-order topological insulators. Finally, we demonstrate that the perfect (imperfect) nature of the fidelity during the time evolution of the system serves as a characteristic signature of a topological (trivial) phase.

Understanding and optimizing the relaxation dynamics of many-body systems is essential both for foundational studies in quantum thermodynamics and for applications such as quantum simulation and quantum computing. Efficient preparation of thermal states of a many-body Hamiltonian is governed by the spectral properties of the associated Lindbladian, in particular its spectral gap, which determines the minimum relaxation rate. In this work, we develop a systematic framework for constructing Lindbladians that prepare thermal states. Our approach reveals a simple relation between the relaxation dynamics at finite and infinite temperatures. The framework is scalable to larger system sizes when implemented using tensor-network methods. We find that efficient thermalization requires that the relaxation dynamics respect the symmetries of the thermal state, which reduces the number of free parameters. By applying gradient-based optimization to the Lindbladians, we enhance the spectral gap and thereby boost thermalization. When applied to both classical and quantum spin models, our method demonstrates a substantial enhancement of the spectral gap. For larger system sizes, our approach provides a variational upper bound and enables a certified lower bound on the spectral gap.

The significance of anomalous Hall effect (AHE) lies in its capability of the interconversion between spin and charge information. The van der Waals (vdW) ferromagnet $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ has attracted extensive interest owing to its high Curie temperature and strong perpendicular magnetic anisotropy. Here, we report a comprehensive Tian-Ye-Jin (TYJ) scaling analysis combined with density functional theory (DFT) calculations to elucidate the origin of the AHE in $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$. We have separated the contributions to the AHE from three distinct mechanisms: skew scattering, side-jump, and intrinsic Berry curvature. Our DFT calculations reveal that the intrinsic contribution is attributed to the transitions between Fe-$d_{xz/yz}$ and Te-$p_{x/y}$ orbitals. Furthermore, we find that electron-magnon scattering significantly influences electrical transport, giving rise to a quadratic dependence between magnetoresistance variation and side-jump scattering. Our findings advance the understanding of AHE and electron-magnon scattering in vdW magnets and would facilitate applications of $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ in spintronic devices.

Altermagnets with spin-layer coupling (SLC) enable symmetry-protected spin splitting without net magnetization. In the SLC altermagnet $\mathrm{Ca}{\left(\mathrm{CoN}\right)}_2$ monolayer, which exhibits distinct sublayer-dependent spin and valley characteristics, we demonstrate that breaking the sublayer-exchange symmetry S via ferromagnetic substrates $({\mathrm{CoCl}}_2 \text{and} \mathrm{CoSe})$ induces robust, magnetization-tunable spin-valley splitting, with the magnitude mainly depending on the strength of interfacial interactions. First-principles calculations reveal that strong interfacial charge redistribution and exchange coupling generate spin-valley splitting for both the valence band maximum (VBM) and conduction band minimum (CBM) of $\mathrm{Ca}{\left(\mathrm{CoN}\right)}_2$. In $\mathrm{Ca}{\left(\mathrm{CoN}\right)}_2/{\mathrm{CoCl}}_2$, antiferromagnetic interfacial exchange produces large spin-valley splitting for CBM but only minor splitting for VBM, with $\mathrm{\Delta }{E}_{\mathrm{V}}=$ −0.016 and 0.019 eV corresponding to upward and downward magnetic orientations of ${\mathrm{CoCl}}_2$, respectively. In contrast, CoSe exhibits ferromagnetic interfacial exchange and pronounced interfacial charge redistribution, forming prominent Co-Se bonding and antibonding states near the Fermi level under opposite substrate magnetic orientations, resulting in larger spin-valley splitting $(\mathrm{\Delta }{E}_{\mathrm{V}}=0.075 \text{and} -0.604 \mathrm{eV})$ consistent with sublayer-resolved band shifts. Device-level spin-transport simulations of the van der Waals (vdW) tunneling junctions further confirm a magnetization-controlled, spin-valley-dependent transport, with $k$-resolved maps revealing anisotropy in transmission coefficients. These results demonstrate that vdW heterostructure engineering provides a promising route for achieving large and magnetization-tunable spin-valley splitting in spintronic and valleytronic devices based on altermagnetic materials.

Magnetic skyrmions extended to three dimensions form stringlike objects whose fundamental role remains largely unexplored. We show that skyrmion strings can terminate on a Néel-type domain wall (DW), realizing a magnetic analog of a Dirichlet(D)-brane soliton. While an isolated Néel DW tends to rotate into a Bloch DW, the Néel DW is stabilized when a skyrmion string ends on it, by being transformed into a trumpet. Unlike field-theory D-branes, the Bloch-type DMI produces linear rather than logarithmic DW bending, and the strings retain finite width far from the DW, circumventing singular behavior. Furthermore, the repulsive interaction between strings allows periodic multijunction solutions, yielding a square lattice of alternating strings and local DW deformations as well as separating Bloch points. These results establish magnetic skyrmion strings as fundamental strings that can end on a D-brane.

We report calorimetric, magnetic, and neutron scattering studies on an $S=5/2$, nearly Heisenberg triangular-lattice antiferromagnet ${\mathrm{K}}_2\mathrm{Mn}{\left({\mathrm{SeO}}_3\right)}_2$ with weak XXZ easy-axis anisotropy. Multiple magnetic phases are identified, including a noncollinear Y phase in zero field, a field-induced collinear $m=1/3$ magnetization plateau, and a high-field V phase. In the Y phase, the magnetic excitation spectrum exhibits both single-magnon excitations and an extended high-energy continuum. Both features are well described by nonlinear spin wave theory. In the field-induced phases, complex effects of the spectrum renormalization even for large $S=5/2$ material are clearly detectable. These results underscore the essential role of magnon-magnon interactions in the dynamics of large-$S$ Heisenberg spin systems on a triangular lattice.

We systematically investigate $g$-factor anisotropy in two-dimensional van der Waals magnets $\mathrm{Cr}{X}_3$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ using broadband magnetic resonance for magnetic ordered states below the critical temperature $\left(T_{\text{cr}}\right)$ and for paramagnetic states above $T_{\text{cr}}$, with varied field orientations. Despite sharing the same layered honeycomb lattice, these compounds exhibit contrasting anisotropies: ${\mathrm{CrCl}}_3$ is an easy-plane antiferromagnet, whereas ${\mathrm{CrBr}}_3$ and ${\mathrm{CrI}}_3$ are easy-axis ferromagnets. From temperature-dependent resonance dispersions with fields applied parallel and perpendicular to the $\mathit{c}$ axis, we uncover opposite trends of $g$-factor anisotropy: $g_{\mathrm{c}}>g_{\mathrm{ab}}$ in ${\mathrm{CrBr}}_3$ and ${\mathrm{CrI}}_3$, but $g_{\mathrm{c}}<g_{\mathrm{ab}}$ in ${\mathrm{CrCl}}_3$. Across the $\mathrm{Cr}{X}_3$ family, both the sign and the magnitude of the $g$ shift are found to correlate closely with the effective anisotropy field, suggesting that magnetic anisotropy provides a useful handle for tuning spin dynamics in van der Waals magnets.

Symmetry constraints determine which physical responses are allowed in a given system. Magnetization induced by strain fields—such as in piezomagnetic and flexomagnetic effects—has typically been studied in materials that break time-reversal symmetry. Here, we propose that nonuniform strain can induce magnetization even in nonmagnetic metals and semiconductors that preserve time-reversal symmetry. This mechanism differs from the conventional flexomagnetic effect: the strain gradient acts as a driving force on the electrons, generating magnetization in a manner closely analogous to current-induced magnetization. Treating the strain field as an external field, we derive a general expression for the magnetization induced by a strain gradient and demonstrate that this response is symmetry-allowed even in time-reversal symmetric systems. We apply our formulation to nonmagnetic systems that lack spatial inversion symmetry while preserving time-reversal symmetry, using a decorated square lattice, monolayer ${\mathrm{MoS}}_2$, and monolayer Janus MoSSe as representative examples. We find a finite magnetization response to strain gradients which is consistent with symmetry arguments, supporting the validity of our theoretical framework. These results offer a pathway for controlling magnetization in nonmagnetic materials using strain fields.

Inertial effects in the stochastic motion of the magnetization of nanomagnets in a uniaxial potential biased by an external field are treated via the corresponding Fokker-Planck equation. This equation can be transformed to a simpler partial differential equation by applying an integral transformation and change of variables. The longitudinal magnetization relaxation function, obtained by solving this equation, simultaneously describes various relaxation modes, namely, a slow interwell mode associated with the reorientation of the magnetization vector through potential barriers, a set of almost degenerate intrawell modes arising due to the motion of the magnetization inside potential wells, as well as a fast relaxation mode caused by the inertia (magnetization nutation). These relaxation modes clearly manifest as three separate bands in the spectrum of the longitudinal component of the magnetic susceptibility tensor. The turnover formula of Mel'nikov and Meshkov is shown to provide a good approximation to the longest relaxation time of the magnetization. Moreover, for small values of the bias field the integral relaxation time has Arrhenius behavior (exponential increase with increasing barrier height), which disappears when the bias field exceeds a critical value.

The temperature dependence of the magnetic moment of bcc α-iron was investigated over the range 300–950 K at pressures of approximately 2 and 6 GPa by in situ neutron powder diffraction. The ${}^{54}\mathrm{Fe}$ isotope, whose neutron scattering length is approximately half that of naturally abundant Fe, was employed to enhance the relative contribution of magnetic scattering. Curie temperatures $\left(T_{\mathrm{C}}\right)$ were determined to be 946(30) K, 838(50) K, and 740(40) K at 2.1, 6.0, and 6.7 GPa, respectively, defining a magnetic phase boundary described by $T_{\mathrm{C}}\left(\mathrm{K}\right)=1043-49\left(7\right)P+1.3\left(1.2\right)P^2$. Upon heating at 6.7 GPa, the α–γ structural transition was observed to follow the magnetic transition. This transition sequence indicates that the magnetic phase boundary lies on the low-temperature side of the α–γ phase boundary. Accordingly, the α–γ transition corresponds to a structural transformation from paramagnetic bcc to paramagnetic fcc iron.

We present fine momentum space resolution resonant elastic x-ray scattering measurements of the magnetic structure of the metallic antiferromagnet ${\mathrm{CoNb}}_3{\mathrm{S}}_6$. Using circular dichroism and full linear polarization analysis of the magnetic scattering, we reveal a noncoplanar double-$\mathit{Q}$ $\left(2Q\right)$ order that is comprised of a noncollinear commensurate component and a long-wavelength incommensurate helical component. This $2Q$ magnetic structure exhibits a staggered scalar spin chirality that forms a modulated stripe like pattern with no uniform component. Measurements of the magnetic structure across many samples reveal a complex domain pattern associated with the magnetic ordering and suggest a lowering of the structural symmetry in ${\mathrm{CoNb}}_3{\mathrm{S}}_6$. We present a symmetry analysis demonstrating that the observed $2Q$ magnetic order breaks all necessary symmetries to enable an anomalous Hall effect and further show how this magnetic order can be naturally explained by four-spin exchange interactions in a metallic magnet. The identification of the magnetic order, associated symmetry breaking, and explanation of its origin provides insight into the mechanism of the unconventional magnetotransport phenomena in ${\mathrm{CoNb}}_3{\mathrm{S}}_6$ and thus can help to determine potential routes for realizing novel electronic phenomena in metallic antiferromagnets.

We introduce time-dependent variational principles to study the nonunitary dynamics of open quantum many-body systems, including dynamics described by the full Lindblad master equation, the non-Hermitian dynamics corresponding to the no-click limit of the fully postselected quantum trajectories, and the dynamics described by a hybrid Lindbladian with a control parameter $\alpha$ which interpolates between the full postselection $(\alpha =0)$ and averaging over all quantum trajectories $(\alpha =1)$. As an application we study the nonunitary dynamics of a lossy or driven-dissipative BCS superconductors, evolving in the presence of two-body losses and two-body pumps. We show that the dynamics in the non-Hermitian limit is qualitatively different than the hybrid dissipative dynamics for any $\alpha >0$, leading to sharp modifications in the universal approach to the driven-dissipative steady states. By considering the dissipative dynamics with pair losses, we show that, as the non-Hermitian limit is approached, the density dynamics evolves from a universal power law to exponential decay that converges towards a quasisteady plateau characterized by the freezing of the particle depletion due to pair losses. The reached quasistationary density increases as a function of the dissipation rate highlighting the emergence of a non-Hermitian Zeno effect in the lossy dynamics. For the driven-dissipative case, the non-Hermitian dynamics skips the infinite temperature steady state reached in the presence of finite contribution of the quantum jumps, and the system can get trapped into an effective negative temperature state. We rationalize these findings in terms of the conservation of the length of the pseudospins which, in the non-Hermitian limit, suppresses the effective single-particle losses and pumps acting on the noncondensed particles.

Andreev bound states are coherent electron-hole superpositions that form in a normal metal through repeated Andreev reflection at a superconducting interface. When the length of a superconducting segment is comparable to the coherence length, the bound states on opposite sides of the segment hybridize through quasiparticle tunneling. In a periodic array, these hybridized Andreev bound states form energy bands below the superconducting gap. We develop a theoretical framework for transport in such Andreev crystals. We demonstrate that, at high interface transparency, a constant phase bias between neighboring superconductors renders the bands directional: one band contains only right-moving and the other only left-moving electronic states. This property leads to a directional conductance that enables the device to operate as a flux- and bias-voltage-tunable filter that allows signal transmission in only one direction.